This invention relates to a probe device and more specifically to a probe device having four data probes equipped with sensors for sensing surface contact in the Z-axis and detecting the surface edge.
In the formation of electronic circuits, integrated circuits may be fabricated from thin semiconductor slices having a multiplicity of matrixes or microcircuits thereon. The general practice is for each slice to contain a multiple of identical repeating matrixes of the same type of microcircuits. The individual unit or circuit is sometimes referred to as an integrated circuit chip or an individual bar.
Before distribution the present practice is to test each of the circuits of each integrated circuit chip on a slice or wafer prior to separating the slice into the desired integrated circuit components or combinations thereof.
Since each microcircuit or integrated circuit of each wafer is normally positioned in a predetermined precise relation with respect to adjacent circuit units, it is possible to test the circuitry if a probe can be accurately located on each preselected point that corresponds to the circuit to be tested. It is possible, for example, to test several different circuits at the same time on any one integrated circuit.
In the test procedure therre are several obstacles to overcome in order to have reliable testing without damaging the slice. One of the difficulties experienced in the use of testing probes which include a supporting body having a needle connected thereto, is that the point of the probe tip may form a scratch on the surface of the semiconductor wafer as it is contacted by the point. This is caused by the lack of an effective Z-axis control. The Z-axis is the direction established by the vertical movement of the chuck with respect to the probe tips. Among other things, the Z-axis control is needed to compensate for surface warpage of slices which may be as much as 5 mils across the surface of a large slice, determining the point of contact with the wafer, and in determining when the probe tips are off the slice i.e. edge detection.
Semiconductor slice testing is performed on a multiprobe machine such as the multiprobe manufactured by Electroglas Corp., Menlo Park, California model 1034X. The multiprobe machine contains a probe card which is a printed circuit board having attached thereto a series of data probes for injecting signals and collecting test data from the semiconductor slice. The present practice includes an edge sensor on the probe card which is in the form of a data probe having an electrical switch mechanism. Operationally the conventional edge sensor functions such that when the probe tip makes contact with the silicon slice an electrical open is caused. This open is detected by the multiprobe system and allows for a continuance of the testing procedures. When the chuck or support block for the semiconductor slice is vertically moved to make contact with the probe tips and no contact is detected by the edge sensor the open condition will not occur and the multiprobe system will perform an indexing procedure and move the slice such that the data probes are over the next row of integrated circuit chips. This conventional edge sensor has been found to be unreliable in the art and the cause of a significant amount of down time of the multiprobe system and damage to chips which results when the chuck is continuously moved upward and probe tip contact is not identified. After the probe tips make contact with the slice it is necessary for the chuck to move an additional 1-5 mils of overtravel in order to break through the oxide layer and make good electrical contact with the active circuit elements, a technique called scrub-in. If the probe contact with the slice is not identified the overtravel cannot be controlled and the result is probe tip breakage, excessive overtravel, which damages chips, and machine down time.
In co-pending application "Method and Apparatus for Determining Probe Contact", Lee Reid, Ser. No. 873,564, filed Jan. 30, 1978 a device is disclosed for edge-sensing and Z-axis control. This device is in the form of a probe having a force sensitive material attached thereto such that when surface contact is made with the probe tip the force distributed over the force sensitive material generates a signal that is detected by an external detector circuit and delivered to a multiprobe system. This device is used to sense the edge of a semiconductor slice having an integrated circuit thereon.
Although the sensor disclosed in the above-identified co-pending application is an improvement over the more mechanical edge sensing device the use of a single edge sensor has inherent problems. The nature of the semiconductor slice is such that the integrated circuits defined thereon are in a pattern series of chips which may be rectangular in geometry. Due to the circular nature of the semiconductor slice there results a series of partial integrated circuit chips on the edges of the semiconductor slice. The use of a single edge sensor will identify approximately half of the partial chips as a surface to be tested and the result is that the multiprobe system will try to test these partial bars, wasting time, identifying the partial bar to be a bad circuit, and thereby inking the partial bar for identification. This series of events results in a loss of time and machine throughput, ink, and possible inking of the support structure, which causes additional wasted time cleaning up.
A further problem is encountered in testing the broken semiconductor slice which gives rise to an increased number of partial chips making edge detection of even greater importance.